The present invention is directed to pharmaceutical compositions formulated so as to have sufficient antimicrobial activity to satisfy the preservation efficacy requirements of the United States Pharmacopeia (“USP”) and analogous guidelines in other countries. The ability to achieve preservation is based on a unique combination of formulation components and particularly the use of two or more different polyols in combination with borate and a preservative, particularly BAC.
Many pharmaceutical compositions are required to be sterile (i.e., substantially free of bacteria, fungi and other pathogenic microorganisms). Examples of such compositions include: solutions and suspensions that are injected into the bodies of humans or other mammals; creams, lotions, solutions or other preparations that are topically applied to wounds, abrasions, burns, rashes, surgical incisions, or other conditions where the skin is not intact; and various types of compositions that are applied either directly to the eye (e.g., artificial tears, irrigating solutions, and drug products), or are applied to devices that will come into contact with the eye (e.g., contact lenses).
The foregoing types of compositions can be manufactured under sterile conditions via procedures that are well known to those skilled in the art. However, once the packaging for a product is opened, such that the composition contained therein is exposed to the atmosphere and other sources of potential microbial contamination (e.g., the hands of a human patient), the sterility of the product may be compromised. Such products are typically utilized multiple times by the patient, and are therefore frequently referred to as being of a “multi-dose” nature.
Due to the frequent, repeated exposure of multi-dose products to the risk of microbial contamination, it is necessary to employ a means for preventing such contamination from occurring. The means employed may be: (i) a chemical agent that prevents the proliferation of microbes in a composition, which is referred to herein as an “antimicrobial preservative”; or (ii) a packaging system that prevents or reduces the risk of microbes reaching a pharmaceutical composition within a container.
Prior multi-dose ophthalmic compositions have generally contained one or more antimicrobial preservatives in order to prevent the proliferation of bacteria, fungi and other microbes. Such compositions may come into contact with the cornea either directly or indirectly. The cornea is particularly sensitive to exogenous chemical agents. Consequently, in order to minimize the potential for harmful effects on the cornea, it is preferable to use anti-microbial preservatives that are relatively non-toxic to the cornea, and to use such preservatives at relatively low concentrations.
Balancing the anti-microbial efficacy and potential toxicological effects of anti-microbial preservatives is sometimes difficult to achieve. More specifically, the concentration of an antimicrobial agent necessary for the preservation of ophthalmic formulations from microbial contamination may create the potential for toxicological effects on the cornea and/or other ophthalmic tissues. Using lower concentrations of the anti-microbial agents generally helps to reduce the potential for such toxicological effects, but the lower concentrations may be insufficient to achieve the required level of biocidal efficacy (i.e., antimicrobial preservation). The use of an inadequate level of antimicrobial preservation may create the potential for microbial contamination.
This balance between anti-microbial efficacy and potential toxicological effects of anti-microbial preservatives is additionally complicated by the fact that many anti-microbial preservatives are ineffective when used in conjunction with some pharmaceutical excipients and/or some pharmaceutical therapeutic agents. For example, some preservatives are rendered less effective when used in conjunction with negatively charged therapeutic agents or excipients.
It has been found that BAC is often desirable as a preservative in conjunction with a wide variety of therapeutic agents and pharmaceutical excipients for situations where other preservatives can be ineffective. It has also been found, however, that BAC can rapidly lose its anti-microbial efficacy when its concentration falls below certain threshold levels. This loss of efficacy is quite unfortunate since concentrations of BAC below these threshold levels can exhibit significantly lower toxicological effects. As such, it would be quite desirable to develop a preservative system that can enhance the anti-microbial effects of low concentrations of BAC such that BAC can be used in situations where other preservatives might be ineffective. Such a system would be particularly desirable for ophthalmic compositions.
Ophthalmic compositions are generally formulated as isotonic, buffered solutions. Particularly desirable ophthalmic compositions are those containing borate or borate-polyol complexes. Examples of such compositions are disclosed in U.S. Pat. Nos. 6,503,497; 6,011,062; 6,849,253; 5,603,929; 5,653,972; 5,849,792; and 5,631,287, all of which are incorporated herein by reference for all purposes.
It is generally known that borate-polyol complexes can be used in ophthalmic compositions to enhance anti-microbial activity in the presence of a preservative such as a polymeric quaternary ammonium; see U.S. Pat. Nos. 5,505,953; 5,811,466; 6,143,799; and 6,365,636, all of which are also incorporated herein by reference for all purposes. It has also been shown that increase in amounts of polyol such as sorbitol or mannitol can significantly increase anti-microbial activity even when relatively low amounts of borate are employed. However, mannitol and sorbitol can also affect the resistance to normalization of tear pH after instillation of the compositions in the eye.
Generally, the borate component (e.g., boric acid) of these complexes can provide the ophthalmic composition with significant resistance to normalization of tear pH. It is generally desirable for these ophthalmic compositions to exhibit at least some degree of buffering so that the natural pH of the compositions does not change significantly over time. However, it is also possible for the compositions to exhibit an undesirably high degree of buffering such that, when applied, they can cause tearing of the eye and discomfort to the eye as the eye attempts to maintain its own pH. Thus, it is desirable to minimize the resistance of the compositions to normalization of tear pH after application. The aforementioned polyols, particularly mannitol, sorbitol or both, can significantly enhance the resistance to normalization of tear pH of the borate component. Thus, for the purpose of maintaining desired levels of buffering, it is typically desirable to maintain relatively low concentrations of these polyols in the presence of borate. However, such lower concentrations can limit or lower the anti-microbial activity of the ophthalmic compositions.
In view of the above, it would be particularly desirable to provide an ophthalmic composition, which includes borate-polyol complex formed with lower concentrations of particular polyols and/or borate and includes low concentrations of BAC while exhibiting improved anti-microbial activity and desirable buffering activity.